Which fck-editor version should i use?

Thank you fck-editor team for constructing this beautyfull editor im really excited about it. I have some questions which I would be delighted if someone could answer:

I am progaming in php and Im confused which version of the editor to use. Are there any benefits in by using fck-editor javascript version instead of php-version? Are there any differences between them?

I aslo wonder how it could be that the javascript version of the editor is able to upload files such as images to the server? Normaly you do not upload things with javascript if you are not using ajax as I understand it.

How it could be that it is possible to interact with the php-version directly in a way that you normaly associate with javascript? How is it possible that the php-version can give me imediate response when typing etc.? Will the php-version work for normal users that do not have php installed on their computer?